In recent years, substantial interest has grown in the bookbinding, publishing and printing industries, and in the graphic arts area generally with respect to the development of improved adhesive compositions which lend themselves to casing-in and casemaking.
Casing-in is typically accomplished using a water based emulsion. During the casing-in process, a book block is laminated to the inside of the cover of a hard bound book by coating the outside of the end sheets of the book block with the adhesive, and then bonding the cover to the end sheets.
Casemaking refers to the production of the case or cover, i.e., the outer shell, of a hard bound book. During this process, the material that forms the outer covering of the book is bonded to binder boards to form a “hard” cover. Typically, the covering material is passed along a conveyor during which time binder boards are mated onto the adhesive coated covering material. The surplus covering material is folded over on to the binder board in a two step process known as “turning in” in which either the sides are folded in first and the ends are folded in second resulting in an overlap of the ends over the sides, or the ends are folded in first and the sides second. These are also called “turn-ins.” Animal glues are typically used for this process, although water based emulsions may also be used.
Conventional water-based casemaking glues and casing-in pastes contain substantial amounts of water, and moisture from these water based systems can be detrimental to a finished book. Moisture from the adhesive can migrate into the binding board or book block causing cockeling or waviness in the end sheets and/or resulting in warpage of the cover. The presence of moisture may also result in curvature of the cover in relation to the book block, as can lack of register of the cover with the book block.
Both hot melt adhesives and reactive hot melt polyurethane adhesives, also referred to as hot melt moisture curing adhesives, which contain no water, have been proposed for use in the bookbinding industry. Use of a hot melt adhesive for casemaking and/or casing-in is described as reducing warpage during the production of the book and as bestowing a degree of resistance to warp during the life of the book.
One problem which has not been addressed by prior art hot melt applications in the casemaking art is the bleed-through which occurs when the case or cover is embossed, and which damages the embossed surface. Whereas cases manufactured using animal glues may be embossed, embossing a case manufactured with the use of a hot melt adhesive is difficult since the adhesive, in contrast to animal glue, tends to flow during the embossing process. This results in letters, figures, designs, etc. which are not clearly identifiable. The current invention addresses this need in the art.